The invention relates to an apparatus for exposing sheet or strip copy material, wherein endless belt conveyors, in frictional contact with the rear side of the copy material, together with the copy material and/or the original, fed to the apparatus in a horizontal plane, are pressed by resilient backing elements, disposed in one plane, against a stationary, planar, translucent rigid plate, the copy material and/or the original are moved through an exposure compartment, which is formed by light elements disposed on the other side of the translucent plate, and pairs of drive rollers, bearing against the upper and lower faces of the copy material and original, are disposed forwardly and rearwardly of the rigid plate, those of the rollers that are presented to the lower face of the copy material, together with at least one further roller, forming the guide and drive rollers for the belts of the conveyor, and the gap between the drive rollers being disposed in the plane of the pressure-applying surface of the translucent plate.
Apparatus of this general kind (as seen for example in Federal Republic of Germany DT-OS 1,522,850) has been developed for the purpose of solving the problem of misalignment between the original and the copy material that occurs in known continuous exposure apparatus which comprise half cylinders and endless belt guide means. This misalignment, caused by the curvature of the cylinders, has rendered such continuous exposure apparatus unsuitable for producing copies that are required to be of very precise size, such as are needed for example in measuring techniques and in the construction of ships, aircraft and automobiles. Since the copies required for the above-mentioned technical purposes are always also very long and wide, the areas of the pressure-applying elements and of the translucent plates have to be correspondingly large in such apparatus; these components are therefore positioned horizontally on very wide and long benches, having a length of 200 to 300 cm or more in the case of copy material having a width of 120 cm. For reasons associated with the static strength and the design of the pressure-applying elements, the copy material, with its coated face downward, and the underlying original can always be placed on the translucent plate and pressed downwards on to the latter by the pressure-applying elements, and exposure has therefore been carried out from below.
In another earlier proposal (Federal Republic of Germany DT-Gbm 1,976,447), the copy material and original are exposed from above while lying on a translucent rigid plate and, by means of a plurality of small-diameter rollers disposed on the upper face of the copy, are pressed against the translucent plate. The copy material and original are then moved across the plate, but the necessary planar application of pressure to the copy material and the original by means of the rollers has been difficult if not impossible to achieve.
Disadvantages common to both known types of apparatus are those of the considerable amount of space required and the very great difficulties in achieving even pressure over all of the considerable area within the exposure compartment since it is not possible, except at the edges, to prevent sagging of the large translucent plate and to prevent it from springing back when pressure is applied; furthermore, the use of plates of suitable thickness would be too expensive and would reduce the amount of light provided. The difficulty of applying uniform pressure has led to the further disadvantages of relatively great expenditure of power for driving the belt because of the large area of friction between the copy material, the original and the pressure-applying or supporting surfaces, with the associated danger of tearing when thinner papers are used, and of inclined travel of the paper web because of uneven pressure distribution under the effect of friction. It has been particularly difficult to move the leading edge of a web of copy material over the entire supporting surface since such movement can only be achieved with the aid of the forward pair of drive rollers and the belt until such time as the rear pair of drive rollers has gripped the leading edge of the web. For this purpose, it is in practice necessary to relax the force of the pressure-applying elements each time, or even to lift them from the surface of the translucent plate. Furthermore, it has of course become possible to accommodate continuous exposure apparatus comprising half-cylinders in a housing which also contains a synchronously operating connected developing apparatus disposed downstream of the exposure apparatus. This is not possible in the case of the above-mentioned known apparatus since this is prevented not only by their size but also by the special means needed for operating them.